Browsing by Author "Rezeau, L."

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    Limitations of multispacecraft data techniques in measuring wave number spectra of space plasma turbulence
    (AGU, 2010-04-10) Sahraoui, F.; Belmont, G.; Goldstein, Melvyn; Rezeau, L.
    Unambiguous determination of spatial properties of space plasma turbulence from temporal measurements has been one of the major goals of the Cluster mission. For that purpose, techniques, such as the k filtering, have been developed. Such multipoint measurement techniques combine several time series recorded simultaneously at different points in space to estimate the corresponding energy density in wave number space. Here we present results of such an analysis, including a detailed discussion of the errors and limitations that arise due to the separation of the spacecraft and the quality of the tetrahedral configuration. Specifically, we answer the following questions: (1) What are the minimum and maximum scales that can be accurately measured given a specific distance between the satellites? (2) How important is the geometry of the tetrahedron, and what is the relationship of that geometry to spatial aliasing? (3) How should one perform a proper integration of the angular frequencies to infer wave number spectra, and what role does the Doppler shift play when the magnetofluid is rapidly convecting past the spacecraft? We illustrate the results with analyses with both simulated and Cluster magnetometer data recorded in the solar wind. We also discuss the potential impact on future multispacecraft missions, such as Magnetospheric MultiScale and Cross-Scale.
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    Three Dimensional Anisotropic k Spectra of Turbulence at Subproton Scales in the Solar Wind
    (APS, 2010-09-23) Sahraoui, F.; Goldstein, Melvyn; Belmont, G.; Canu, P.; Rezeau, L.
    We show the first three dimensional (3D) dispersion relations and k spectra of magnetic turbulence in the solar wind at subproton scales. We used the Cluster data with short separations and applied the k-filtering technique to the frequency range where the transition to subproton scales occurs. We show that the cascade is carried by highly oblique kinetic Alfvén waves with ωₚₗₐₛ≤ 0.1 ωcᵢ down to k⊥ρᵢ∼ 2. Each k spectrum in the direction perpendicular to B₀ shows two scaling ranges separated by a breakpoint (in the interval [0.4,1]k⊥ρᵢ): a Kolmogorov scaling k⊥⁻¹.⁷ followed by a steeper scaling ∼k⊥⁻⁴.⁵. We conjecture that the turbulence undergoes a transition range, where part of the energy is dissipated into proton heating via Landau damping and the remaining energy cascades down to electron scales where electron Landau damping may predominate.